Messages in this thread Patch in this message |  | | From | Morten Rasmussen <> | Subject | [PATCH v5 4/6] sched/fair: Avoid pulling tasks from non-overloaded higher capacity groups | Date | Fri, 14 Oct 2016 14:41:10 +0100 |
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For asymmetric cpu capacity systems it is counter-productive for throughput if low capacity cpus are pulling tasks from non-overloaded cpus with higher capacity. The assumption is that higher cpu capacity is preferred over running alone in a group with lower cpu capacity.
This patch rejects higher cpu capacity groups with one or less task per cpu as potential busiest group which could otherwise lead to a series of failing load-balancing attempts leading to a force-migration.
cc: Ingo Molnar <mingo@redhat.com> cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> --- kernel/sched/fair.c | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 28e42cb41d7b..a5efafda23ef 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7069,6 +7069,17 @@ group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs) return false; } +/* + * group_smaller_cpu_capacity: Returns true if sched_group sg has smaller + * per-cpu capacity than sched_group ref. + */ +static inline bool +group_smaller_cpu_capacity(struct sched_group *sg, struct sched_group *ref) +{ + return sg->sgc->min_capacity * capacity_margin < + ref->sgc->min_capacity * 1024; +} + static inline enum group_type group_classify(struct sched_group *group, struct sg_lb_stats *sgs) @@ -7172,6 +7183,20 @@ static bool update_sd_pick_busiest(struct lb_env *env, if (sgs->avg_load <= busiest->avg_load) return false; + if (!(env->sd->flags & SD_ASYM_CPUCAPACITY)) + goto asym_packing; + + /* + * Candidate sg has no more than one task per cpu and + * has higher per-cpu capacity. Migrating tasks to less + * capable cpus may harm throughput. Maximize throughput, + * power/energy consequences are not considered. + */ + if (sgs->sum_nr_running <= sgs->group_weight && + group_smaller_cpu_capacity(sds->local, sg)) + return false; + +asym_packing: /* This is the busiest node in its class. */ if (!(env->sd->flags & SD_ASYM_PACKING)) return true; -- 2.7.4
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